Probabilistic aspects of high-dynamic compressive failure of cementitious materials

Abstract

When subjecting cementitious materials to high-dynamic uniaxial compression, the ultimate load carrying capacity of tested specimens increases significantly with increasing loading rate. In the present paper, an engineering mechanics model [6,7] which explains high-dynamic strengthening of cement pastes, mortars, and concretes under uniaxial compression is discussed. The model explains that high dynamic strengthening is probabilistic in the sense that the first crack may nucleate at any position within the volume of the tested specimen, and that the actual position of crack nucleation is relevant for the achievable compressive strength of the specimen. The disintegration process of the specimen, namely, starts with nucleation of the first crack and lasts until the crack has propagated-in loading direction-through the entire specimen. This process lasts the longer, the closer the first crack nucleates to one of the load platens. During the disintegration process, the stress level increases inside the solid parts of the specimens, driven by progressive macroscopic load increase. Crack nucleation is modeled by an elastic limit criterion. Crack propagation is considered to happen under mode I, in direction of uniaxial loading, at the speed of Rayleigh waves. The ultimate load is equal to the product of the elastic stress rate and the total test duration. The model does not include any fitting parameters. Still, model predictions agree qualitatively and quantitatively very satisfactorily with measured dynamic strength increase factors. This suggests that high-dynamic strengthening is a purely structural effect, depending on geometric properties of the tested specimen.